how to convert each column data type in data.frame

convert_datatype_in_df.R

# set function with which convert data into named vector
col.type.f <- c(vane=as.factor,
              prefecture=as.factor,
              date=as.Date,
              time=as.factor,
              ts=as.POSIXct)

# convert data type
for (col in names(col.type.f)) {
  f.conv <- col.type.f[col][[1]]
  dt[col] <- f.conv(dt[,col])
}